Today, many enterprises run applications on virtual machines (VMs). VM mobility, both live and offline, can provide enormous flexibility and also bring down operating expense costs. However, both live and offline migration of VMs is still typically limited to within a local network because of the complexities associated with cross subnet live and offline migration. These complexities mainly arise from the hierarchical addressing used by various layer 3 routing protocols. For cross data center VM mobility, virtualization vendors usually require that the network configuration of the new data center where a VM migrates must be similar to that of the old data center. This severely restricts widespread use of VM migration across data center networks.
For offline migration, some limitations can be overcome by reconfiguring IP addresses for the migrated VMs. However, even this effort is non-trivial and time consuming as these IP addresses are embedded in various configuration files inside these VMs.